Packing Sheets with Webpack

Webpack is a modern build tool for generating static sites. It has a robust JavaScript-powered plugin system¹

SheetJS is a JavaScript library for reading and writing data from spreadsheets.

This demo uses Webpack and SheetJS to pull data from a spreadsheet and display the content in an HTML table. We'll explore how to load SheetJS in a Webpack 5 Asset Plugin and generate data for use in webpages.

The "Webpack 5 Demo" creates a complete website powered by a XLSX spreadsheet.

This demo covers static asset imports. For processing files in the browser, the "Bundlers" demo includes an example of importing the SheetJS library in a browser script.

Webpack 5 Asset Module

Webpack 5 supports asset modules. With a special option, the loader will receive NodeJS Buffers that can be parsed. The dev server will even watch the files and reload the page in development mode!

The SheetJS NodeJS module can be imported from Webpack loader scripts.

The following diagram depicts the workbook waltz:

flowchart LR
  file[(workbook\nfile)]
  subgraph SheetJS operations
    buffer(NodeJS\nBuffer)
    aoo(array of\nobjects)
  end
  html{{HTML\nTABLE}}
  file --> |webpack.config.js\ncustom rule| buffer
  buffer --> |sheetjs-loader.js\ncustom plugin| aoo
  aoo --> |src/index.js\nfrontend code| html

Webpack Config

The Webpack configuration is normally saved to webpack.config.js.

Required Settings

module.rules is an array of rule objects that controls module synthesis.² For the SheetJS Webpack integration, the following properties are required:

test describes whether the rule is relevant. If the property is a regular expression, Webpack will test the filename against the test property.
use lists the loaders that will process files matching the test. The loaders are specified using the loader property of the loader object.

The following example instructs Webpack to use the sheetjs-loader.js script when the file name ends in .numbers or .xls or .xlsx or .xlsb:

webpack.config.js (define loader)
// ...
module.exports = {
  // ...
  module: {
    rules: [
      {
        /* `test` matches file extensions */
        test: /\.(numbers|xls|xlsx|xlsb)$/,
        /* use the loader script */
        use: [ { loader: './sheetjs-loader' } ]
      }
    ]
  }
};

Recommended Settings

It is strongly recommended to enable other Webpack features:

resolve.alias defines path aliases. If data files are stored in one folder, an alias ensures that each page can reference the files using the same name³.
devServer.hot enables "hot module replacement"⁴, ensuring that pages will refresh in development mode when spreadsheets are saved.

The following example instructs Webpack to treat ~ as the root of the project (so ~/data/pres.xlsx refers to pres.xlsx in the data folder) and to enable live reloading:

webpack.config.js (other recommended settings)
// ...
module.exports = {
  // ...
  resolve: {
    alias: {
      /* `~` root of the project */
      "~": __dirname
    }
  },
  // ...
  /* enable live reloading in development mode */
  devServer: { static: './dist', hot: true }
};

SheetJS Loader

The SheetJS loader script must be saved to the script referenced in the Webpack configuration (sheetjs-loader.js).

As with ViteJS, Webpack will interpret data as UTF-8 strings. This corrupts binary formats including XLSX and XLS. To suppress this behavior and instruct Webpack to pass a NodeJS Buffer object, the loader script must export a raw property that is set to true⁵.

The base export is expected to be the loader function. The loader receives the file bytes as a Buffer, which can be parsed with the SheetJS read method⁶. read returns a SheetJS workbook object⁷.

The loader in this demo will parse the workbook, pull the first worksheet, and generate an array of row objects using the sheet_to_json method⁸:

sheetjs-loader.js (Webpack loader)
const XLSX = require("xlsx");

function loader(content) {
  /* since `loader.raw` is true, `content` is a Buffer */
  const wb = XLSX.read(content);
  /* pull data from first worksheet */
  var data = XLSX.utils.sheet_to_json(wb.Sheets[wb.SheetNames[0]]);
  return `export default JSON.parse('${JSON.stringify(data)}')`;
}

/* ensure the function receives a Buffer */
loader.raw = true;

/* export the loader */
module.exports = loader;

Asset Imports

Spreadsheets can be imported using the plugin. Assuming pres.xlsx is stored in the data subfolder, ~/data/pres.xlsx can be imported from any script:

src/index.js (main script)
import data from '~/data/pres.xlsx';
/* `data` is an array of objects from data/pres.xlsx */

const elt = document.createElement('div');
elt.innerHTML = "<table><tr><th>Name</th><th>Index</th></tr>" +
  data.map((row) => `<tr>
    <td>${row.Name}</td>
    <td>${row.Index}</td>
  </tr>`).join("") +
"</table>";
document.body.appendChild(elt);

Webpack 5 Demo

Tested Deployments

This demo was last tested on 2024 April 06 against Webpack 5.91.0

Initial Setup

Create a new skeleton project:

mkdir sheetjs-wp5
cd sheetjs-wp5
npm init -y
npm install webpack@5.91.0 webpack-cli@5.1.4 webpack-dev-server@5.0.4 --save
mkdir -p dist
mkdir -p src
mkdir -p data

Install the SheetJS NodeJS module:

npm i --save https://cdn.sheetjs.com/xlsx-0.20.3/xlsx-0.20.3.tgz

Save the following to dist/index.html:

dist/index.html
<!DOCTYPE html>
<html>
  <head>
    <title>SheetJS + Webpack 5</title>
  </head>
  <body>
   <script src="main.js"></script>
  </body>
</html>

Save the following to src/index.js:

src/index.js
import data from '~/data/pres.xlsx';

const elt = document.createElement('div');
elt.innerHTML = "<table><tr><th>Name</th><th>Index</th></tr>" +
  data.map((row) => `<tr>
    <td>${row.Name}</td>
    <td>${row.Index}</td>
  </tr>`).join("") +
"</table>";
document.body.appendChild(elt);

Save the following to webpack.config.js:

webpack.config.js
const path = require('path');

module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'main.js',
    path: path.resolve(__dirname, 'dist'),
  },
  devServer: {
    static: './dist',
    hot: true,
  },
  resolve: {
    alias: {
      "~": __dirname
    }
  },
  module: {
    rules: [
      {
        test: /\.(numbers|xls|xlsx|xlsb)$/,
        use: [ { loader: './sheetjs-loader' } ]
      }
    ]
  }
};

Save the following to sheetjs-loader.js:

sheetjs-loader.js
const XLSX = require("xlsx");

function loader(content) {
  /* since `loader.raw` is true, `content` is a Buffer */
  const wb = XLSX.read(content);
  /* pull data from first worksheet */
  var data = XLSX.utils.sheet_to_json(wb.Sheets[wb.SheetNames[0]]);
  return `export default JSON.parse('${JSON.stringify(data)}')`;
}
/* ensure the function receives a Buffer */
loader.raw = true;
module.exports = loader;

Download https://docs.sheetjs.com/pres.xlsx and save to the data folder:

curl -L -o data/pres.xlsx https://docs.sheetjs.com/pres.xlsx

Live Reload Test

Open the test file data/pres.xlsx in a spreadsheet editor like Excel.
Start the development server:

npx webpack serve --mode=development

The terminal will print URLs for the development server:

<i> [webpack-dev-server] Project is running at:
<i> [webpack-dev-server] Loopback: http://localhost:8080/

Open the Loopback address (http://localhost:8080) in a web browser.

It should display a table of Presidents with "Name" and "Index" columns

Add a new row to the spreadsheet (set A7 to "SheetJS Dev" and B7 to 47) and save the file.

After saving the file, the page should automatically refresh with the new data.

Static Site Test

Stop Webpack and build the site:

npx webpack --mode=production

The final site will be placed in the dist folder.

Start a local web server to host the dist folder:

npx http-server dist

The command will print a list of URLs.

Open one of the URLs printed in the previous step (http://localhost:8080) and confirm that the same data is displayed.

To verify that the page is independent of the spreadsheet, make some changes to the file and save. The page will not automatically update.

To verify that the data was added to the page, append main.js to the URL (http://localhost:8080/main.js) and view the source. The source will include president names. It will not include SheetJS library references!

See "Plugins" in the Webpack documentation. ↩
See module.rules in the Webpack documentation. ↩
See resolve.alias in the Webpack documentation. ↩
See "Hot Module Replacement" in the Webpack documentation. ↩
See "Raw" Loader in the Webpack documentation. ↩
See read in "Reading Files" ↩
See "Workbook Object" ↩
See sheet_to_json in "Utilities" ↩

Webpack 5 Asset Module​

Webpack Config​

Required Settings​

Recommended Settings​

SheetJS Loader​

Asset Imports​

Webpack 5 Demo​

Initial Setup​

Live Reload Test​

Static Site Test​

Footnotes​